Dimethyl ether powered engine

ABSTRACT

An internal combustion engine that is driven by dimethyl ether (DME) and a storage and delivery system for the DME that will reduce considerably the emissions of NO x  and particulate. Existing internal combustion engines, fueled by conventional fuels can be economically converted to the use of DME as a fuel.

BACKGROUND OF THE INVENTION

Air pollution is a serious problem especially in large cities. In theU.S. the Environmental Protection Agency has the primary responsibilityfor carrying out the requirements of the Clean Air Act, which specifiesthat air-quality standards shall be established for hazardoussubstances. There are also state laws and international Protocols thatset standards.

Some air pollutants are formed through the action of sunlight onpreviously emitted reactive materials (called precursors). For example,ozone, a pollutant in smog, is produced by the interaction ofhydrocarbons and nitrogen oxides under the influence of sunlight.Although many types of combustion contribute to this problem, trucks andbuses have been identified as a significant source of both oxides ofnitrogen (NO_(x)) and particulate matter (PM). Pollution from internalcombustion engines has been significantly reduced by burning the fuel ascompletely as possible, by recirculating fumes and by using catalyticconverters. However, standards are constantly being changed in anattempt to lower exhaust emissions. Current standards propose NO_(x)emissions limits of between 1.5 and 2 grams per brake horse power perhour (g/bhp-hr). The state of California has adopted an Ultra LowEmission Vehicle (hereinafter ULEV) regulation, which will becomeeffective in 1998, for medium-duty vehicles that limits NO_(x) plushydrocarbons at 2.5 g/bhp-hr and caps particulates at 0.05 g/bhp-hr. Inaddition this California regulation restricts the emissions offormaldehyde (HCHO) to 0.025 g/bhp-hr and Carbon Monoxide (CO) emissionsto 7.2 gbhp-hr. Meeting such standards will be difficult for sparkignited (SI) engines and even more difficult.

Trying to meet such standards alternative fuels such as Methanol andEthanol have been tried. Dimethyl ether, CH₃ -O-CH₃ hereinafter DME, iscurrently used as a propellant for spray cans. DME was adopted for thisuse as a replacement for chlorofluorcarbons. DME has been used inexperiments, as an ignition enhancer, for Methanol-fueled DieselEngines. However, even when the ratio of DME to Diesel Fuel is as nighas 60%, satisfactory operation was not obtained. Recently, a limitedtest was conducted using pure DME as an alternative fuel in a singlecylinder, four stroke, direct injection Diesel Engine. This test yieldedvery promising combustion, performance and emissions results. Althoughthe fuel injection system used in this test was designed for standarddiesel fuel, when using DME the thermal efficiency of the engine wasequivalent to when diesel fuel is used. Furthermore, as compared tostandard diesel fuel the NO_(x), were low and the smoke emissions wereextremely low. Reference is made to a soon to be published paper by S.C. Sorenson entitled, Performance and Emissions of a 0.273 Liter DirectInjection Diesel Engine with a New Alternative Fuel, in which this testare discussed.

The use of DME as an alternative fuel does have obstacles that must beovercome. DME is a gas at ambient temperature and pressure and thus thefuel storage and delivery system must be pressurized to maintain the DMEin a liquid state. DME must be pressurized to about five bar to keep itin a liquid state under ambient conditions. At the elevated temperaturespresent on an internal combustion engine higher pressures (12-30 bar)are required to maintain DME in a liquid state.

The energy density of DME, although higher than the alternative fuelsMethanol (CH₃ OH) and Ethanol (CH₃ -CH₂ OH) it is much lower thanconventional Diesel Fuel. As a result to obtain the same power from anengine fueled by DME obtained when fueling with Diesel Fuel the volumeof DME must be increased by a factor of about 1.8. To accommodate thisincreased volume the fuel injector must have a larger orifice opening. Asingle hole pintle type nozzle, rather than a multi hole nozzle, hasbeen found to function well to provide this increased fuel flow.

A fuel's Cetane number, which is a measure of the fuel's ability toauto-ignite, has an important influence on diesel combustion and is ameaningful indicator of a fuel's value for diesel engines. Fuels with ahigh Cetane number will ignite quicker and thus will have a shortignition delay. This lowers premixed burning of the fuel, which in turnlowers NO_(x) and noise emissions. DME has a higher Cetane number thanDiesel Fuel and thus it will ignite quicker and will have a relativelyshort ignition delay. By throttling the amount of fuel injected duringthe initial portion of the injection cycle the quantity of fuel in thecombustion chamber when ignition occurs has been diminished whichsignificantly lowers NO_(x) and noise emissions. The mechanism forthrottling the fuel injected during the initial portion of the injectioncycle should be time dependent such that it can be coordinated withignition delay that is also time dependent.

Also, the vapor pressure of DME is higher than most other fuels. At 38°Centigrade, the vapor pressure of DME is 8 bar as compared to 0.0069 barand 0.35 bar respectively for Diesel fuel and Methanol. Thus DME willboil at a lower atmosphere pressure than Diesel fuel or Methanol. Thesystem must be pressurized to prevent the fuel from flashing to vapor inthe engine's fuel manifolds or fuel injection system.

The viscosity of DME is estimated to be about 5% to 10% of diesel fuel.This relatively low viscosity of DME portends fuel leakage in a systemdesigned for fuels having higher viscosities. Thus, standard fuelstorage and delivery systems will not be suitable for DME.

Test results, such as those described in the above referred to Sorensonpaper, are obtained in carefully controlled and monitored operatingenvironments and conditions. It is often difficult to duplicate suchtest results outside the laboratory. As a result further developmentsare required to obtain the same results in a production situation wheremany and changing conditions are experienced.

Internal combustion engines and especially Diesel engines representlarge capital investments and have long useful lives. The currentprocess for producing DME would result in a price that would render itunacceptable as an alternative fuel. A new less costly manufacturingmethod has been developed to produce "raw DME" which is a form of DMEthat includes small amounts of water and Methanol. Large capitalinvestments would be required to build the necessary facilities toproduce raw DME at volumes that would meet its demand as an alternativefuel. Even greater capital investments would be required to provide thenecessary refueling system. Large capital investments of this magnitudeare unlikely to be made if the alternative fuel can only be used innewly produced special designed engines. Thus, a very importantconsideration for an alternative fuel is whether economic fieldconversions can be made to existing engines to enable them to use thealternative fuel.

For these reasons, there is a need for a fuel storage and deliverysystem that will enable internal combustion engines to be powered withDME fuel in a broad range of environmental conditions. The new andimproved fuel storage and delivery system must also permit existinginternal combustion engines to be economically converted in the field tobe fueled by DME.

SUMMARY OF THE INVENTION

The present invention is directed to the use of DME as a fuel ininternal combustion engines and a DME storage and delivery system forinternal combustion engines. Experimental work done by Sorenson yieldedtest results that suggest that the use of DME as an alternative fuel forinternal combustion engines may enable the current ULEV standards to bemet or even exceeded. This invention will enable the test results seenin the laboratory work described in the Sorenson paper to be achieved inproduction internal combustion engines that operate in many conditionsand in environments that are constantly changing. The present inventionwill also enable existing engines fueled by conventional fuel to beeconomically converted to use DME as a fuel.

The present invention is directed to a fuel storage and delivery systemincluding a fuel pump that has low internal leakage to accommodate thelow viscosity of the DME.

The injector of this invention utilizes a pintle type nozzle that canprovide the increased volume of DME fuel required in the same cylinderrotation arc required in an engine using diesel fuel.

This invention uses a characteristic of the pintle nozzle, to graduallyincrease its orifice area as the nozzle is lifted, to damp the fuel flowduring the initial portion of the injection cycle. This improvedinjector, with damping, can be used with engines using diesel fuels andalso engines that are powered by DME.

The injection system of this invention controls the rate at which theDME is injected and thus reduces the premixed fuel quantity and avoidsnoisy combustion and high NO_(x) emissions.

The nozzle orifice area of this invention is relatively large toaccommodate for the lower density and heating value of DME.

This invention provides flexible injection timing to optimize the tuningof the engine and gain low emissions.

For the foregoing reasons there is a need for a DME storage and deliverysystem for internal combustion engines that will enable the favorableemission properties of DME to be exploited in new and existing engines.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an embodiment of the invention in which acommon rail injection system is provided for the DME.

FIG. 2 is a detailed, partially cut away, view of an embodiment of aunit injector.

FIG. 3 is a perspective view of the damping piston of FIG. 2.

FIG. 4 is a lift/time diagram illustrating the nozzle needle lift withand without the damper.

FIG. 5 is a lift/time diagram illustrating the effect of high and lowviscosity fluid.

FIG. 6 is a detailed view of an embodiment of a pintle nozzle in theclosed position.

FIG. 7 is a detailed view of the pintle nozzle of FIG. 6 in a slightlyraised or open position.

FIG. 8 is a detailed view of the pintle nozzle of FIG. 6 in a greaterraised or open position then shown in FIG. 7.

FIG. 9 is a detailed view of the pintle nozzle of FIG. 6 in a fullyraised or open position.

FIG. 10 is cross sectional view of a unit injector, of the typedisclosed in FIG. 2, mounted in the injector cavity of a conventionalengine.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

There is shown in FIG. 1 a schematic view of an embodiment of theinvention in which the fuel for an internal combustion engine is storedin a pressurized fuel tank 10 from which it is fed by a pump 14 to arail 22 which functions as an accumulator system from which fuel isdistributed to unit injectors 40. DME must be pressurized to about 5 barto keep it in a liquid state under ambient conditions. At the elevatedtemperatures present on an internal combustion engine the fuel tank 10should be pressurized to about 9 bar to insure that the DME ismaintained in a liquid state.

The fuel pump 14 must be able to provide DME to the rail 22 at apressure in the range of 100-300 bar. The fuel supply pump 14 can bedriven by the engine, at a speed ratio of engine speed to pump speed inthe range of 1:1 to 1:0.5. Pump 14 must have the capacity to meet theengine's peak torque requirements. At peak torque an engine is rotatingat a relatively high rate, and accordingly drives the fuel pump at arelatively high rate. At this relatively high speed a gear type pumpwould have high efficiency even when pumping DME which has a very lowviscosity. The viscosity of DME is about 10% of the viscosity of Dieselfuel. Thus, a gear type pump would perform adequately when the engine isoperating at peak torque speeds. However, another critical requirementfor the fuel pump 14, is that it must be able to supply sufficient fuelto the engine during start-up. At start-up the engine and therefore thepump 14 will be running at a relatively low speed. A diesel engine thatdelivers peak torque at speeds of 2,000 rpm will have a start-up speedof about 200 rpm. At 200 rpm the efficiency of a gear type pump will bevery low and inadequate to start the engine when pumping a fluid havinga viscosity as low as that of DME. The low speed combined with the lowviscosity of DME fuel affords time for the fuel to leak internallyaround the gears of the pump. This internal leakage is an inefficiencyin the pump and if it is too high the pump can't manage the criticalengine start-up requirements. As the engine speed add the correspondingpump speed increases there is less time for internal leakage andconsequently there is less leakage. For these reasons a highly efficientpump is necessary when using DME as a fuel. A piston type pump withseals to minimize leakage, that has an efficiency of about 50% atstarting speed when pumping DME has been found suitable.

A filter 12 and a shut-off valve 13 are provided in the line 11 thatextends from the fuel tank 10 to the pump 14. The Rail PressureModulator Valve (RPMV) 18 functions to control the output pressure ofthe pump 14 that determines the pressure of the DME in the common rail22. The RPMV also functions as a relief valve to prevent DME, at excesspressures, from being sent to the rail 22. A pressure transducer 16 isprovided in the line 15 that extends from the pump 14 to the rail 22. Aswill be discussed in more detail, transducer 16 can be used to monitorthe rail pressure and transmit data back to the ECM through a line 23.

A common rail 22, which dispenses fuel to all of the engine's cylinders,is necessary to ensure a constant fuel pressure to all injectors. InFIG. 1 the rail 22 has been illustrated to have eight fuel passages 21.It should be understood that if the rail 22 is being used on a four orsix cylinder engine the rail would have one passage 21 for eachcylinder. Although the rail 22 is shown as a separate component it couldbe an integral part of the engine.

One unit injector 40 has been illustrated in FIG. 1, however it shouldbe understood that there is a unit injector 40 for each of the engine'scombustion cylinders. The body of the injector 40 has an upper bore 44that extends longitudinally from its upper end as seen in FIG. 1. Theupper bore 44 is closed by a plug 48 at its upper end. A damping piston70 is contained in the chamber 67 defined by the upper bore 44 and theplug 48. There is silicone fluid 120 or other suitable viscous fluid inthe chamber 67. The fuel passage 21 from the rail 22 is secured to aside extension 38 of the injector 40 such that the DME fuel enters theinjector through an inlet passage 36. An injector solenoid 30 is carriedby the extension 38, which when energized opens a valve 32 that isnormally held closed by a spring 34 or by a magnetic force. When thevalve 32 is opened by the solenoid 30, the DME fuel flows through theinlet passage 36 into the fuel passage 50 that extends longitudinallythrough the body of the injector 40. Injector 40 carries a pintle nozzle90 at its bottom end, as seen in FIG. 1. An optional fuel return ventline 24 can be provided.

The Electronic Control Module (ECM) 20 includes a microprocessor thatreceives inputs from various engine monitors such as fuel temperature,fuel rail pressure, throttle position, engine revolutions per minute andcam angle. The ECM 20 is programmed with the operating strategy of thesystem and controls the operation of the entire fuel system. Otherengine conditions that can be monitored and imputed to the ECM are, forexample, oil temperature, ambient air temperature, barometric pressureand exhaust back pressure. The pressure transducer 16 in line 15 is anexample of one such monitor.

The ECM 20 computes output control signals 19 and 17. The outputssignals 17 are sent to the solenoids 30 and cause the solenoids to beactuated at a precise time. Output control signal 17 determines the timefor starting fuel injection and the duration of each injection.

The output signal 19 represents the desired rail pressures for thespecific engine conditions calculated according to the operatingstrategy of the system and in response to the data collected by thevarious monitors. Signal 19 is directed to a Rail Pressure ModulatorValve (RPMV) 18. The RPMV 18 functions to control the output pressure ofthe pump 14 that determines the pressure of the DME in the common rail22.

Referring now to FIGS. 2 through 9 the injector 40 will be discussed inmore detail.

The injector 40 includes a generally cylindrical shaped body portion 42.The injector 40 disclosed herein conforms to the shape and dimensions ofa standard 17 millimeter injector that is currently used in dieselengines available from most engine sources. Thus existing conventionaldiesel engines can receive injector 40 by simply replacing theconventional injectors. The other modifications necessary to convert aconventional diesel engine from diesel fuel to DME are relatively minorand it will be possible to convert existing diesel engines to DME fuel.

The injector 40 has been provided with a pintle type nozzle 90, at itsbottom or first end, rather than a multi hole nozzle. The single holedesign feature of a pintle nozzle functions well to provide theincreased fuel flow necessary when using DME. Pintle type nozzles havethe characteristic of increasing the flow area as the pintle is lifted.This feature is best illustrated in FIGS. 6 through 9. In FIG. 6 a firstbeveled portion 92 of the pintle nozzle 90, located at the discharge endof the pintle nozzle, is seated on a corresponding beveled portion 56 ofthe body 42 and the flow area is zero and accordingly there is no flow.It should be noted that there is a slight clearance between thecorresponding cylindrical portions of the pintle and body below thefirst beveled portion 92 and the beveled portion 56. In FIG. 7 thepintle 90 has been lifted slightly, indicated by the letters PL, and theorifice, indicated by the letter 0, has opened slightly. In FIG. 8 thepintle 90 has been further lifted and the flow area of the orifice hasincreased. In FIG. 9 the pintle 90 is fully lifted and the flow area ofthe orifice is at its maximum.

Referring now to FIG. 2, lifting of the pintle nozzle 90 will bedescribed. The pressurized DME fuel enters the injector 40, at the topor second end of the injector body 42, through the inlet passage 36 whenthe injector solenoid 30 is energized and flows longitudinally through afuel passage 50 formed in the injector body 42. Fuel passage 50 opensinto a cavity 58. The pintle nozzle 90 includes first and second pistonlike portions 94 and 96 respectively that slide in correspondingcylindrical bores in the injector body 42 to thus guide and allow thepintle nozzle 90 to reciprocate longitudinally in the injector body 42.First piston like portion 94 is of a smaller diameter than second pistonlike portion 96 and these piston like portions are connected by a secondbeveled portion 98. The second beveled portion 98 of the pintle nozzleis located in the cavity 58 and when the pressurized DME fuel enterscavity 58 it exerts a force on the second beveled portion 98, acomponent of which is directed upward. This upward directed force liftsthe pintle nozzle. The upper end of the pintle nozzle extends into alower bore 46 formed in the injector body 42 where it bears against aspring seat 60 biased downwardly by a spring 64. The upper end of spring64 engages the top surface of the lower bore 46. The upper portion ofthe spring seat 60 is in contact with the lower end of a lower push rod52 that slides in a cylindrical opening 62 that connects the upper bore44 with the lower bore 46. The upper end of lower push rod 52 extendedthrough a seal 66, secured to the bottom surface of the upper bore 44,and bears against the bottom surface of the damping piston 70. Thevolume of the upper bore 44 that is not occupied by the damping piston70 if filled with silicone fluid 120 or other suitable viscous fluid. Anupper push rod 54 bears against the circular top surface 74 of thedamping piston 70 and extends into a bore 68 formed in the plug 48. Theupper end of upper push rod 54 engages a spring 69 contained in the bore68. Spring 69 exerts, through the upper push rod 54, a downward force onthe damping piston 70.

An isolated perspective view of the damping piston 70 is shown in FIG.3. The damping piston 70 has a generally cylindrical shape and includesa flat circular top surface 74. A pair of rectangular shaped flatsurfaces 76 are formed on opposite sides of the damping piston 70. Theflat surfaces 76 do not extend to the top circular surface 74 and thereremains part of the damping piston at its upper end that is a completecylinder. The damping piston 70 and upper bore 44 are dimensioned toallow the damping piston 70 to reciprocate with a close slidingrelationship in the upper bore 44. The longitudinal length of the truecylinder portion is represented by L in FIG. 3. As shall be discussed inmore detail the duration of the throttling of the fuel injection duringthe initial portion of the injection can be controlled or changed byutilizing damping pistons 70 in which the dimension L is different.

A damping orifice 72, is formed by a bore having a relatively smalldiameter that extends from the top surface 74 to the bottom surface ofthe damping piston 70.

A reverse flow check valve 75 is provided in the damping piston 70 by abore 78 having a larger diameter than the diameter of the dampingorifice 72. At the top surface 74 the flow check valve bore 78 isenlarged to form a check ball cage. When the damping piston 70 is beingforced upward through the silicone fluid the check ball 77 seats andcloses the bore 78 and thus prevents silicone fluid from passing throughthe bore 78. However, when the damping piston 70 moves downward thesilicone fluid can pass upward through the bore 78 raising the checkball 77 off its seat. The check ball 77 is retained in the enlargedportion of bore 78 by the check ball cage but permits free passage ofthe silicone fluid. When the damping piston 70 moves downwardly, thesilicone fluid 120 is also free to pass unencumbered through the dampingorifice 72.

When the damping piston 70 is forced into the silicone fluid, above thedamping piston, the silicone fluid is forced to flow through the dampingorifice 72. Thus upward movement of the damping piston 70 and the pintlenozzle is slowed or restricted. As the damping piston 70 raises in upperbore 44 a distance equal to the dimension L, the flats 76 becomeuncovered which opens a path for the silicone fluid to flow from abovethe damping piston 70 to below the damping piston 70. This ends dampingand the velocity of the damping piston 70 and the pintle nozzleincreases. The pintle nozzle lift L at which the flats 76 are exposedcan be varied by using a damping piston 70 having a different dimensionL.

FIG. 4, is a graph plotting pintle nozzle lift on the Y axis and time onthe X axis. The thin line on the graph represents the lift over time fora pintle nozzle that is not damped and the heavy line represents thelift over time for a pintle nozzle that is damped. The lift of thepintle nozzle with damping is gradual to the point where the flats 76are exposed at which point the lift is accelerated until maximum lift isachieved.

The velocity of the pintle nozzle lift can be adjusted by using siliconefluids having different fluid viscosities. FIG. 5 is a graph in whichpintle nozzle lift is shown on the Y axis and time on the X axis. Inthis graph the thin line represents a low viscosity silicone fluid andthe heavy line represents a high viscosity silicone fluid. This graphillustrates that as the viscosity of the silicone fluid is increased thethrottling or damping effect on the lift increases. This graph alsoillustrates, through the broken lines, how the combination of usingsilicone fluids of different viscosity and changing the length ofdimension L effects the lift of pintle nozzle. Thus, the lift of thepintle nozzle can be customized for a particular engine or environment.

FIG. 10 shows a cross section of a conventional cylinder head 100 thathas a common rail 22, of the type previously described, secured theretoby bolts 102. An injector 40 incorporating the invention of this patentis mounted in the conventional injector aperture 104. A fuel passageline 21 is shown extending from the common rail to the injector 40. Theinjector portion of this invention has been built into a standard sizeinjector body that can be inserted into the standard size injectoraperture that is found in many existing diesel engines. In addition thisFigure shows that the injector of this invention could be mounted in aconventional diesel engine that is fueled by conventional diesel fuel.When the injector of this invention is used in an engine fueled bydiesel fuel, the concept of damping the initial portion of the injectioncycle will reduce the NO_(x) and the noise pollution.

While the invention has heretofore been described in detail withparticular reference to an illustrated apparatus, it is to be understoodthat variations, modifications and the use of equivalent mechanisms canbe effected without departing from the scope of this invention. It is,therefore, intended that such changes and modifications are covered bythe following claims.

What is claimed is:
 1. An internal combustion engine of the type thatincludes at least one combustion cylinder, a fuel storage tank, anaccumulator connected to the fuel storage tank by a conduit and a fueldelivery system for delivering fuel from the accumulator to said atleast one combustion cylinder wherein the improvement comprises:saidinternal combustion engine being fueled by dimethyl ether; means forpressurizing said fuel storage tank; an engine driven fuel pump in saidconduit that has the capacity to deliver fuel, during engine start-up,to said accumulator at a pressure in the range of 100-300 bar; a fuelinjection system including a unit injector which injects said dimethylether directly into for said at least one combustion cylinder, saidinjector including a nozzle that can vary the fuel flow rate as afunction of injection pressure, said unit injectors including a solenoidthat controls injection timing and the duration of the injection cycle.2. The invention as set forth in claim 1 wherein said nozzle is a pintlenozzle that moves axially in response to pressurized fuel.
 3. Theinvention as set forth in claim 1 wherein said engine driven fuel pumpis a piston type pump including seals to minimize leakage, said pistontype pump having an efficiency of about 50% at engine start-up speed. 4.The invention as set forth in claim 1 wherein said unit injectorcomprising an elongated cylindrical shaped body having a first end and asecond end, said elongated cylindrical shaped body including a beveledportion at its first end;said elongated cylindrical shaped bodyincluding a fuel inlet passage that is controlled by a fuel inlet valve;a solenoid carried by said elongated cylindrical shaped body foractuating said fuel inlet valve to initiate a fuel injection cycle; apintle nozzle mounted for reciprocal movement in said first end of saidelongated cylindrical shaped body, said pintle nozzle including adischarge end having a first beveled portion, a first piston likeportion of a given diameter, a second piston like portion of a diametergreater than said give diameter and a second beveled portion connectingsaid first and second piston like portions; a cavity formed in saidelongated cylindrical shaped body in the area of said second beveledportion of said pintle nozzle, a fuel passage formed in said elongatedcylindrical shaped body connecting said fuel inlet passage and saidcavity such that when pressurized fuel enters the fuel inlet passage andflows through the fuel passage to said cavity the pressurized fuelexerts a force on the second beveled portion of the pintle nozzlecausing it to move relative to the elongated cylindrical shaped bodysuch that said first beveled portion of said pintle nozzle moves awayfrom said beveled portion of said elongated cylindrical shaped body toopen the nozzle orifice; a damping device in said injector thatfunctions to resist or throttle the opening of the nozzle orifice duringthe initial stage of the fluid injection cycle.
 5. The invention as setforth in claim 2 wherein said fuel injection system includes a dampingdevice that functions to retard the axial movement of said pintle nozzleduring the initial portion of the injection cycle.
 6. The invention asset forth in claim 2 wherein said engine driven fuel pump is a pistontype pump including seals to minimize leakage, said piston type pumphaving an efficiency of about 50% at engine start-up speed.
 7. Theinvention as set forth in claim 5 wherein said engine driven fuel pumpis a piston type pump including seals to minimize leakage, said pistontype pump having an efficiency of about 50% at engine start-up speed. 8.An internal combustion engine that uses dimethyl ether as a fuel, saidengine including a plurality of combustion cylinders and a fuel storageand delivery system, said fuel storage and delivery system, comprising:apressurized fuel storage tank, an accumulator system connected by aconduit to said pressurized fuel storage tank, an engine driven fuelpump in said conduit that has the capacity to deliver fuel from saidpressurized fuel storage tank to said accumulator system at a pressurein the range of 100-300 bar; a fuel injection system including anelectronically controlled unit injector for injecting fuel into eachcombustion cylinder, a cylinder inlet conduit extending from saidaccumulator system to each combustion cylinder, each unit injectorincluding a solenoid that is activated to control injection timing andduration, a nozzle mounted for movement in said unit injector inresponse to the presence of pressurized fuel to open an orifice into thecombustion chamber, said orifice when fully opened will supplysufficient fuel flow to achieve full load power and maintain thermalefficiency, each unit injector including a damping device that retardsthe initial movement of said nozzle toward the fully open orificeposition to restrict initial fuel flow which lowers the NO_(x) and noiseemissions.
 9. The invention as set forth in claim 8 wherein said nozzleis a pintle nozzle that moves axially in response to pressurized fuel.10. The invention as set forth in claim 8 wherein said engine drivenfuel pump is a piston type pump including seals to minimize leakage,said piston type pump having an efficiency of about 50% at enginestart-up speed.
 11. The invention as set forth in claim 8 wherein saidunit injector comprising an elongated cylindrical shaped body having afirst end and a second end, said elongated cylindrical shaped bodyincluding a beveled portion at its first end;said elongated cylindricalshaped body including a fuel inlet passage that is controlled by a fuelinlet valve; a solenoid carried by said elongated cylindrical shapedbody for actuating said fuel inlet valve to initiate a fuel injectioncycle; a pintle nozzle mounted for reciprocal movement in said first endof said elongated cylindrical shaped body, said pintle nozzle includinga discharge end having a first beveled portion, a first piston likeportion of a given diameter, a second piston like portion of a diametergreater than said give diameter and a second beveled portion connectingsaid first and second piston like portions; a cavity formed in saidelongated cylindrical shaped body in the area of said second beveledportion of said pintle nozzle, a fuel passage formed in said elongatedcylindrical shaped body connecting said fuel inlet passage and saidcavity such that when pressurized fuel enters the fuel inlet passage andflows through the fuel passage to said cavity the pressurized fuelexerts a force on the second beveled portion of the pintle nozzlecausing it to move relative to the elongated cylindrical shaped bodysuch that said first beveled portion of said pintle nozzle moves awayfrom said beveled portion of said elongated cylindrical shaped body toopen the nozzle orifice; a damping device in said injector thatfunctions to resist or throttle the opening of the nozzle orifice duringthe initial stage of the fluid injection cycle.
 12. The invention as setforth in claim 9 wherein said engine driven fuel pump is a piston typepump including seals to minimize leakage, said piston type pump havingan efficiency of about 50% at engine start-up speed.
 13. The inventionas set forth in claim 11 wherein said engine driven fuel pump is apiston type pump including seals to minimize leakage, said piston typepump having an efficiency of about 50% at engine start-up speed.
 14. Amethod of fueling an internal combustion engine with dimethyl ethercomprising the steps of:(a) storing the dimethyl ether in a pressurizedfuel storage tank; (b) pumping the dimethyl ether from the pressurizedfuel storage tank to an accumulator; (c) controlling the pumping of thedimethyl ether to achieve a pressure in the accumulator that is withinthe range of 100-300 bar; (d) actuating unit injectors in timed sequenceand for pre-determined durations to initiate the opening of the injectororifice through which dimethyl ether flows directly to the combustioncylinders; and (e) retarding the initial opening of said orifice torestrict the initial fuel flow during the initial portion of theinjection cycle and thereby lower the NO_(x) and noise emissionsemanating from the internal combustion engine.
 15. An internalcombustion engine that uses dimethyl ether as a fuel, said engineincluding a plurality of combustion cylinders and a fuel storage anddelivery system, said fuel storage and delivery system, comprising:apressurized fuel storage tank, an accumulator system connected by aconduit to said pressurized fuel storage tank, a fuel pump in saidconduit that has the capacity to deliver fuel from said pressurized fuelstorage tank to said accumulator system, said pump being a piston typepump including seals to minimize leakage, said pump having an efficiencyof about 50% at engine start-up speed, a fuel injection system includingan electronically controlled unit injector for injecting fuel into thecombustion cylinder, a cylinder inlet conduit extending from saidaccumulator system to each combustion cylinder, each unit injectorincluding a solenoid that is activated to vary injection timing andduration, a nozzle mounted for movement in each unit injector that inresponse to the presence of pressurized fuel opens an orifice into thecombustion chamber, said orifice being of a size that when fully openedwill supply sufficient fuel flow to achieve full load power and maintainthermal efficiency, each unit injector including a damping device thatretards the initial movement of said nozzle toward its fully openposition to restrict initial fuel flow which lowers the NO_(x) and noiseemissions.